1. Field of the Invention
This invention relates to a network, a packet switching network, a packet switching system, and network management equipment which efficiently process a large amount of connectionless data traffic using a connection-oriented network such as an ATM network.
2. Description of Related Art
Recently, as the Internet has rapidly evolved, networks and switching systems which efficiently process a large amount of connectionless data traffic with the use of a connection-oriented network, such as an ATM network, have been offered. `Connectionless` means that data is sent without first setting up a connection to the destination, while `connection-oriented` means that data is sent after setting up a connection to the destination.
For example, the MPOA protocol architecture is described on page 121 in "ATM Internetworking" (Nikkei BP Publishing Center Inc.; First edition, Sep. 22, 1995). MPOA is an abbreviation for Multi Protocol ATM. When communicating via the MPOA, an ATM address generated at the MPOA server by converting the layer-3 destination address (for example, destination IP (Internet Protocol) address) is obtained and then an ATM connection is set up using the ATM signaling protocol. Note that the ATM connection used in the protocol is an SVC (Switched Virtual Connection) which is set up on a request-basis when there is data traffic to be sent. The signaling protocol for an SVC is described, for example, in "ATM Forum UNI version 3.1" (Prentice-Hall, Inc.: 1995).
Another communication protocol is an RSVP (Resource Reservation Protocol) described in "RSVP: A New Resource ReSerVation Protocol" (September 1993 number of IEEE Network). The RSVP requires that the receiver sequentially reserve communication bandwidth, a router, a buffer, and other resources for a data path between the sender and the receiver. After the resources have been reserved, data is sent.
A typical connection-oriented communication is a telephone. This communication requires real-time software processing, called call admission control, and resource reservation. Once the resources are reserved, the communication bandwidth, usually the bi-directional bandwidth, is guaranteed. In this communication mode, because the resources are not released even when there is no traffic, the resource usage efficiency is low.
On the other hand, in connectionless communication which is used primarily for LANs, the resources are reserved for each burst of data. This communication is suited for sending a large amount of data instantaneously in one direction only. However, because the communication bandwidth is not always guaranteed in this communication, resource contention occurs as the whole resource usage ratio becomes high. In addition, because data which could not be sent because of insufficient resources must be resent, the resources become more insufficient and, as a result, congestion may result.
ATM was introduced to solve these two problems. ATM contributes to the efficient use of resources. However, ATM still has the two problems described above. That is, ATM still requires complex call admission control and, in addition, results in congestion when the resources become insufficient.
Ideally, all communications should be done via ATM to take full advantage of ATM. However, telephones, LANs, and WANs (Wide Area Network) are used in real time communications and, therefore, the shift of all the communication facilities to those of ATM is not so easy. Because more and more traffic is expected over these networks in future, ATM networks must co-exist with conventional data communication networks.
As the term LAN implies, emphasis has been placed on local communication in the conventional data communication. Recently, however, the need for global communication, such as the Internet, has arisen. In such global communication, an error at a single site in the connectionless communication mode may cause other sites to resend data, one after another, and may cause immediate congestion around the world. This requires a large network to manage resources (such as bandwidth allocation) and to manage a large amount of resources hierarchically.
The above description deals primarily with the problems with the "quantity" and the "scale" of data communication. We must also consider the problems with "quality." As communication finds its way into our lives, a need has arisen for a variety of services using the telephone network, including automatic message transfer, sender's number indication, collect call, and teleconferencing. To meet these needs, intelligent networks have been built in the telephone network for efficient control signal communication. It is expected that the same need will also arise for data communication. In data communication networks, intelligent networks may also be used as with telephone networks, or a virtual network may be built logically in an ATM network to take full advantage of its characteristics. However, the conventional LAN-oriented data communication networks are not fully compatible with ATM networks, meaning that in a large data communication network, various operations must be performed. For example, in a large data communication network, the user must keep track of data traffic, control communication bandwidths dynamically, or provide additional information on services. Also included in the quality features are the network error isolation function and the congestion prevention function.
The following describes in more detail the problems this invention will try to solve.
When communicating via MPOA, a request-based ATM connection is set up in the SVC mode when there is a data traffic to be sent. Therefore, the data transfer delay time is increased by the time needed to set up an ATM connection. In the worst case, the ATM connection time may be longer than the data transfer time. In addition, when many users generate data and set up request-based connections, many control packets for connection setup and disconnection are transferred before and after actual data transfer. This may result in network congestion.
On the other hand, when communicating via RSVP, the data transfer delay and the delay variation become large because the resources must be reserved before data is sent. In addition, the need to hold the resources such as bandwidth requires the sender to send a refresh packet at a regular interval for holding the resources. Therefore, when there are many users who generate data, the communication of control packets necessary for resource reservation uses a lot of bandwidth, making network management more complex.